U P 2008 12.09 1 Special Topicm Coune
January 8
- 22,3008
Mamwhumettm Inmtitute of Technology
2.
3.
4.
5.
6.
Introduction to Terrestrial Impact
Cratering
Review of Some Major Research
Studies of Terrestrial Impact
Craters
Tools of Analysis
Impact Crater: Chesapeake Bay
Well Logging and Geochemical
Studies
Impact Cratering: Economic
Potential and Environmental Effects
Conclusion
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
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January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
The course work involves the following:
January 8, 10, 15, 17, 22 10 AM to Noon
5 sessions each of 2 hours
25%
Study/work assignments – 4
20%
Project
Literature Survey &
Writing a report
30%
Project Presentation
25%
Required percentage to pass this course is
95%
Grading: P/F
3
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
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January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
Chesapeake Bay Impact Structure
Hydrogeological study:
Geophysical Well Logging Investigation
| Geochemical Study:
North American Tektite Investigation
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5
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Regional map of Chesapeake Bay Impact Crater
can be seen in the USGS Open File Report 20071094.
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
| Chesapeake Bay Impact Crater
Virginia, USA
| Latitude N 37° 17'
| Longitude W 76° 1'
| Diameter 90.00 km
| Age
35.5 ± 0.3 Ma
6
CHESAPEAKE BAY IMPACT STRUCTURE
Chesapeake Bay impact structure formed
●
●
●
●
about 35 million years ago,
during the late Eocene period,
a comet fragment or asteroid struck the
U.S. Atlantic continental shelf
currently the area is the southern part of
Chesapeake Bay & adjacent land masses in the
Virginia Coastal Plain.
The impact structure
●
approximately circular,
● 53-mile-diameter crater,
● centered near the town of Cape Charles,
Va.
| Materials within the structure currently
exist beneath hundreds of feet
of younger Cenozoic marine sediments.
(65 Ma to Present)
|
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
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7
The scientific community has been studying
Chesapeake Bay impact crater, impact event
and its effects
|
Early 1980s - Glomar Challenger deep-sea cores
containing the crater’s ejecta off Atlantic City,
New Jersey.
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
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January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
Information about the Chesapeake Bay impact
structure is available in numerous published studies
such as:
| Koeberl and others
(1996),
| Poag
(1997),
| Powars and Bruce
(1999),
| Powars
(2000),
| Edwards et al
(2004),
| Poag et al (2004),
| Horton and others(2005),
| Gohn et al
(2007).
9
The following discussion is based on the USGS Report
by
G. S. Gohn, W. E. Sanford, D. S. Powars, J. W. Horton,
Jr., L. E. Edwards, R. H. Morin, and J. M. Self-Trail,
Site report for USGS test holes drilled at Cape
Charles, Northampton County, Virginia, in 2004
USGS Open-File Report 2007–1094.
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
The purpose of the discussion is to understand
what is involved in geophysical well logging and
and its use in the hydrogeologic study.
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The Chesapeake Bay impact structure spatially coincides with a
well used inland zone of salty ground water.
This spatial association strongly suggests a genetic association
(Powars and Bruce, 1999; McFarland and Bruce, 2005).
The presence of the inland salt-water zone has practical
significant effect on the increasing demand on fresh water
supply by the rapid population and commercial growth in areas
above and near to the salt-water zone. (Emry and Miller, 2004).
Detailed knowledge of the distribution of the salt-water zone and
its formative processes are important to determine whether
increased ground-water pumping in adjacent areas will lead to
migration of the salt water. [Horton and others (2005a, b)]
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
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11
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
Geophysical logging was conducted (Gohn, 2004) in four
stages, to total depth up to 2,699 ft.
Well logging tools:
1) Caliper,
2) Multifunction tool,
3) Full-waveform sonic velocity probe,
4) Neutron porosity probe
The principles of operation of these logging tools are well
described (Hearst et al, 2000)
A composite of the geophysical logs collected and analyzed
from test hole USGS-STP2 is given in Figure 5, USGS
Open-File Report 2007–1094 (Gohn et al 2004)
12
1) Measurement of borehole diameter by caliper
¾
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The caliper log provides information about
uniformity of the bore hole
the mechanical strength of
the bore hole materials.
Log displays significant enlargements in
borehole diameter within the postimpact
sediments and the sediment-clast breccia that
extend well beyond bit gauge.
Significant variation in the sediment (borehole)
diameter is indicative of a very unstable and
mechanically weak geologic materials.
Improvement of the conditions are seen
markedly below 2,150 ft in the more competent
breccia-gneiss section, and the replacement of
the drilling bit with the coring bit near 2,440 ft
is recognized as a step reduction in diameter at
2,444 ft.
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
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1) Measurement of borehole diameter by caliper …
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below 2,150 ft
breccia-gneiss section,
near 2,440 ft is recognized as a step
reduction in diameter
Figure based on "Composite of geophysical
logs obtained in test hole USGS-STP2", Gohn
et al 2004.
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
Figure shows
Depth vs. Borehole diameter
variation
| enlargements in borehole diameter
within
1) the post-impact sediments
2) the sediment-clast breccia
indicating
very unstable borehole
mechanically weak geologic
materials.
14
2) The multifunction tool measurement
Sometimes borehole fluid conductivity and
temperature data may not be useful under the
field conditions because of the significant
disturbances by drilling.
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
Multifunction tool measures
natural gamma activity,
electrical resistivity,
borehole fluid conductivity,
borehole fluid temperature.
15
2) The multifunction tool – gamma activity measurement
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
The gamma-activity log is a measure of natural gamma
radiation being emitted by the surrounding rocks and
sediments.
Clays accumulate radioisotopes through adsorption and ionexchange processes, high gamma activity are indicative of
clay rich zones.
Feldspathic sandstones, phosphatic limestones, and
glauconitic sands also are associated with high gamma
responses.
Two zones that displayed increased gamma counts
lower part of the postimpact sediments (940 ft to 1,150 ft)
upper part of the breccia-gneiss section (2,150 ft to 2,220 ft).
16
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
17
Figure based on Figure 7, Gohn et al 2004.
2) The multifunction tool – electrical resistivity measurement
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
Resistivity profiles are effective in identifying freshwaterseawater interfaces.
Electrical resistivity measurements consist of short-normal
(16-inch) and long normal (64-inch) resistivities, also
referred to as near and far resistivities, respectively.
Saturated formation resistivity is primarily a function of
porosity, pore-fluid resistivity, and mineralogy, typically
correlating positively with grain size and negatively with
porosity.
A lower resistivity corresponds to higher porosity or to
smaller grain size. The understanding is that surface area
associated with fine particles promotes the transmission
of electric current (Biella and others, 1983; Kwader, 1985).
18
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
19
Figure based on “Composite of geophysical logs obtained
in test hole USGS-STP2”, Gohn et al 2004.
3. Full-waveform sonic velocity measurement
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
The full-waveform sonic tool is equipped with a variable
frequency transmitter and three receivers.
The measurements consist of :
| Gathering the logs at a frequency of 10 kHz.
| Processing them by means of a semblance technique (Paillet
and Cheng, 1991) to estimate sonic velocities.
| Plotting of compressional - wave velocity VP (solid line) vs.
shear-wave velocity VS (dashed line)
| It is difficult to have sufficient energy transmission into the
surrounding rocks to generate a detectable shear wave in all
but the hardest rocks.
| Thus, the plot of VS gets limited to only the lower most brecciagneiss section, where VS is roughly half the velocity of VP.
These values fall within a well-constrained lithology band
presented by Paillet and Cheng (1991).
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3. Full-waveform sonic velocity measurement …
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Figure based on "Composite of geophysical logs obtained
in test hole USGS-STP2", Gohn et al 2004.
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
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Figure shows log of the
compressional-wave velocity
vs. depth to 2,440 ft.
The log is clearly identifying the
delineation and the contact between the
postimpact sediments
The log is indicating that the value of
VP in the sediments approaches
thatof water alone (~ 1.55 km/s),
underlying sediment-clast breccia
at 1,163 ft.
Below this contact, the compressionalwave velocities gradually increase
downward in the sediment-clast breccia.
Below 2,150 ft, VP increases to almost 5
km/s as the rocks become more
indurated and mechanically competent,
due to poor sampling conditions
(borehole enlargements, mud invasion)
21
4) Neutron porosity measurement
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
The neutron probe estimates saturated formation
porosity.
| Specially designed test pits are used to calibrate
the neutron detector . The response of the neutron
detector, in counts per second, can be accurately
converted to quantitative values of total porosity.
The formation should be saturated.
| This estimate of total porosity includes both free
water and bound water on clay surfaces.
|
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4) Neutron porosity measurement
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Figure based on "Composite of geophysical logs
obtained in test hole USGS-STP2", Gohn et al 2004.
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
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The figure shows
Porosity vs. Depth
The porosity log shows a marked
shift at the sediment-breccia
contact (1,163 ft)
The log clearly distinguishes
between the high-porosity
postimpact marine sediments
(porosity ~ 60 percent) and the
underlying sediment-clast breccia
(porosity ~ 20 percent).
The porosity estimates for the
postimpact sediments are in the
range of roughly 50 to 65 percent,
23
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
(Powars and Bruce, 1999; Powars, 2000; Gohn et al 2007):
Marine, glauconitic, shelly sands of late Paleocene
age compose the Aquia aquifer, which is regionally
extensive but only a minor ground-water supply
resource.
Generally similar, but finer-grained
sediments of late Paleocene to early Eocene age
compose the overlying Nanjemoy-Marlboro
confining unit.
Both hydrogeologic units are
truncated along the margin of the Chesapeake Bay
impact crater.
24
“Sediments of late Eocene age compose three newly
designated confining units that overlie the Potomac
aquifer within the Chesapeake Bay impact crater.
These confining units include, from bottom to top, the
impact-generated, lithologically distinctive but highly
variable Exmore clast and Exmore matrix confining
units and the marine, clayey Chickahominy confining
unit. The three confining units collectively impede
ground-water flow across the crater.”
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
(Powars and Bruce, 1999; Powars, 2000; Gohn et al 2007):
25
The Piney Point aquifer is regionally extensive, overlying most of
the Chesapeake Bay impact crater and beyond, but is only locally
significant as a ground-water supply resource across the middle
reaches of Northern Neck and the Middle and York-James
Peninsulas.
Acknowledgement
A large amount of detailed information on the Chesapeake
Bay impact crater was provided by the U.S. Geological
Survey (USGS) Eastern Earth Surface Processes Team in
support of understanding the effects of the impact crater on
ground-water resources. Conceptualization of geologic relations
of the crater was particularly aided by David S. Powars
of the USGS.
|
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
(Powars and Bruce, 1999; Powars, 2000; Gohn et al 2007):
26
January 17, 2008: IAP 2008 12.091
SESSION 4: P.ILA
What are tektites?
■ Tektites are glass bodies.
■ They are produced during hypervelocity impact
events.
■ Near-surface lithologies will be ejected from the
source center melting during an early stage of
cratering .
■ The ejected material will be deposited in
geographically and stratigraphically defined strewn
fields, very far from their point of origin.
Ref: Shaw and Wasserburg 1982;
Horn et al. 1985; Glass 1990; Koeberl 1994)
27
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
Tektite Formation
■ impact angles 30° - 50° seem to be most favorable
for tektite production are impact angles
■ initial travel velocities the molten materials are in
order of 10 km/second in the expanding vapor
plume.
■ final settling velocities are around tens of meters
per second,
■ tektites are formed during cooling with
characteristic features.
Ref:
Artemieva (2002)
28
Age
Ma
Source
Crater
1
Autraliasian
0.79
Not
Identified
2
Ivory Coast
1.07
Bosumtwi,
Ghana
3
Central
European
15
Ries,
Germany
4
North
American
35.5
Investigating
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
Tektite strewn
fields
29
Refer to p. 690,
Figure 1. The global distribution of ejecta material
in the Upper Eocene (according to Simonson and
Glass 2004) and the locations of the Popigai and
Chesapeake Bay impact craters,
by
Deutsch, A., and Koeberl, C.,
Meteoritics & Planetary Science 41,
Nr 5, 689–703, 2006.
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
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January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
Observations
| Major and trace element chemical compositions of the
Chesapeake Bay target sediments, in comparison with
the Exmore breccia (crater fill) and tektite data, do not
allow us to uniquely identify a specific source for the
North American tektites.
| For refractory and lithophile elements, including the
REEs, the similarity between the tektites and the
Chesapeake Bay crater rocks is the greatest, within a
factor of about two.
| Tektites are mainly derived from surficial sediments, well
known (from studies of the other three
strewn fields (e.g., Montanari and Koeberl 2000 )
31
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
Observations …
| It is interesting to note that the Na content of at least the
bediasites is higher than that of all
analyzed sediments, necessitating source materials as
rich in sodium as a precursor to the tektites.
| Sample suite did not include any upper Eocene
sediments that were present on or near the target
surface in the Chesapeake Bay area because such
rocks are not preserved.
| In addition, most or all of the target area was covered by
shallow ocean water (Poag et al. 2004).
| Thus, there could have been some contamination of the
tektites from sea water residue, e.g., sodium.
| This is also indicated by boron isotopic data of
bediasites (Chaussidon and Koeberl 1995).
32
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
Observations …
| Quite different from the well constrained isotopic
parameters of the heterogeneous target at the Popigai
impact structure (Kettrup et al. 2003), which was
formed nearly contemporaneous with the Chesapeake
Bay structure.
| Existing isotope data for tektites and spherules as well
as published and new data for target
rocks substantiate that indeed two (and not more) ejecta
layers with different source craters are present in the
stratigraphic
column, deposited within a very short interval of 20 kyr
(or less).
33
addition, most or all of the target area
was covered by shallow ocean water (Poag
et al. 2004).
| Thus, there could have been some
contamination of the tektites from sea water
residue, e.g., sodium.
| This is also indicated by boron isotopic data
of bediasites (Chaussidon and Koeberl
1995).
January 17, 2008: IAP2008 12.091 SESSION 4: P.ILA
| In
34
CHUR - Chondritic Uniform Reservoir
εSr t = 35.7 Ma
= deviation of 87Sr/86Sr ratio with respect to CHUR
εΝd t = 35.7 Ma
= deviation of 143Nd/144Nd ratio with respect to CHUR
January 17, 2008: IAP2008 12.091 SESSION 4: P.ILA
Sr-Nd Isotopic Data
35
January 17, 2008: IAP2008 12.091 SESSION 4: P.ILA
Conclusion:
| The Exmore breccia (crater fill) can be explained as
a mix of the measured target sediments and the
granite, plus an as-yet undetermined component.
| The post-impact sediments of the Chickahominy
formation have slightly higher TNd CHUR model
ages of about 1.55 Ga, indicating a contribution of
some older materials.
36
εSr t = 35.7 Ma of
εNd t = 35.7Ma of
|
+54 to +272, and
-6.5 to -10.8;
A granitic basement sample with a TNd CHUR
model age of 1.36 Gy have
εSr t = 35.7 Ma of +188 and an
εNd t = 35.7Ma of −5.7.
January 17, 2008: IAP2008 12.091 SESSION 4: P.ILA
Conclusion …
| The unconsolidated sediments, Cretaceous to
middle Eocene in age, have
37
εSr t = 35.7 Ma of
εNd t = 35.7Ma of
+104 to +119, and
-5.7
for
0.47 Ga (TSr UR), and 1.15 Ga (TNdCHUR).
The εSr and εNd are summarized (in the following)
Table.
January 17, 2008: IAP2008 12.091 SESSION 4: P.ILA
Conclusion …
| Newly analyzed bediasites have the following
isotope parameters:
38
εNd
Unconsolidated sediments,
Cretaceous to middle Eocene
in age
+54 to +272
-6.5 to -10.8
A granitic basement sample with
a TNd CHUR model age of 1.36 Ga
+188
−5.7
Newly analyzed bediasites
0.47 Ga (TSr UR), and 1.15 Ga
(TNdCHUR).
+104 to +119
-5.7
t = 35.7 Ma
Ref: Deutsch, A., and Koeberl, C., 2006
t = 35.7Ma
January 17, 2008: IAP2008 12.091 SESSION 4: P.ILA
εSr
Sr-Nd
Isotope Data
39
January 17, 2008: IAP2008 12.091 SESSION 4: P.ILA
Conclusion …
| Using the geographic position as well as age and
chemical data, previous studies have suggested
that the Chesapeake Bay impact structure is the
source of the North American tektites (Poag et al.
1994; Koeberl et al. 1996).
| The Sr-Nd isotope data for samples from the
Chesapeake Bay structure establishes a clear
correlation between this impact structure and the
35 Ma tektites and the associated microtektites
from the North American strewn field.
40
January 17, 2008: IAP2008 12.091 SESSION 4: P.ILA
Artemieva, N. A.,
Tektite origin in oblique impacts: Numerical modeling
of the initial stage. In Impacts in Precambrian
shields, edited by Plado J. and Pesonen L. J., pp.
257–276, 2002,
Berlin: Springer, 2002,
ISBN 978-3540435174.
| Biella, G., Lozej, A., and Tabacco, I.,
Experimental study of some hydrogeophysical
properties of unconsolidated porous media,
Ground Water, 1983, v. 21, no. 6, pp. 741-751.
|
41
De Verteuil, L., and Geoffrey, N.,
Miocene dinoflagellate stratigraphy and systematics of
Maryland and Virginia,
Micropaleontology, 1996, v. 42, supplement, 172 p.,
ISBN 0-913424-42-0.
|
Deutsch, A., and Koeberl, C.,
Establishing the link between the Chesapeake Bay
impact structure and the North American tektite
strewn field: The Sr-Nd isotopic evidence,
Meteoritics & Planetary Science 41, 2006, Nr. 5, 689–
703.
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
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Edwards L. E., Horton J. W., Jr., and Gohn G. S.,
ICDP-USGS workshop on deep drilling in the central crater
of the Chesapeake Bay impact structure, Virginia, USA:
Proceedings volume. Reston, Virginia: U.S. Geological
Survey, Open-File Report 2004-1016, CD-ROM.
|
Emry, S.R., and Miller, B.,
Chesapeake Bay impact structure – 35 million years after –
and still making an impact, in
Edwards, L.E., Horton, J.W., Jr., and Gohn, G.S., 2004,
ICDP-USGS Workshop on deep drilling in the central crater
of the Chesapeake Bay impact structure, Virginia, USA,
September 22-24, 2003: U.S. Geological Survey Open-File
Report 2004-1016, CD-ROM.
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
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Horn P., M¸ller-Sohnius D., Kˆhler H., and Graup G.,
Rb-Sr systematics of rocks related to the Ries crater, Germany,
Earth and Planetary Science Letter, 1985, v. 75, pp. 384–392.
|
Glass B. P.,
North American tektite debris and impact ejecta from DSDP Site
612.
Meteoritics, 1989, v. 24, pp. 209–218.
|
Glass B. P. 1990.
Tektites and microtektites: Key facts and interferences.
Tectonophysics, 1990, v.171, pp. 393–404.
|
Hearst, J.R., Nelson, P.H., and Paillet, F.L.,
Well Logging for Physical Properties,
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
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2nd ed., John Wiley & Sons, New York, 483 p, 2000.
ISBN: 978-0471963059
44
|
Horton, J.W., Jr., Aleinikoff, J.N., Kunk, M.J., Gohn,
G.S., Edwards, L.E., Self-Trail, J.M., Powars, D.S.,
and Izett, G.S., 2005a, Recent research on the
Chesapeake Bay impact structure, USA – Impact
debris and reworked ejecta, in Kenkmann, T., Hörz,
F., and Deutsch, A. eds., Large meteorite impacts III:
Geological Society of America Special Paper 384, p.
147-170.
Horton, J.W., Jr., Powars, D.S., and Gohn, G.S., eds.,
2005b, Studies of the Chesapeake Bay impact
structure – The USGS-NASA Langley corehole,
Hampton, Virginia, and related coreholes and
geophysical surveys: U.S. Geological Survey
Professional Paper 1688-A-K, 453 p.
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
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January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
Horton, J.W., Jr., Gohn, G.S., Jackson, J.C.,
Aleinikoff, J.N., Sanford, W.E., Edwards, L.E., and
Powars, D.S., 2005c, Results from a scientific test
hole in the central uplift, Chesapeake Bay impact
structure, Virginia, USA [abstract]: Lunar and
Planetary Science Conference XXXVI, Abstract 2003,
2 p.
| Koeberl C.
Tektite origin by hypervelocity asteroidal or
cometary impact: Target rocks, source craters, and
mechanisms,
In Large meteorite impacts and planetary evolution,
edited by Dressler B. O., Grieve R. A. F., and
Sharpton V. L. Boulder,Colorado:
Geological Society of America, 1994, pp. 133–151.
|
46
Kettrup B., Deutsch A., and Masaitis V. L.,
Homogeneous impact melts produced by a
heterogeneous target? Sr-Nd isotopic evidence from the
Popigai crater, Russia.
Geochimica et Cosmochimica Acta , 2003, v. 67, pp. 733–
750.
|
McFarland, E. R., and Bruce, T.S., 2005,
Distribution, origin, and resource-management
implications of ground-water salinity along the western
margin of the Chesapeake Bay impact structure in
eastern Virginia, in Horton, J.W., Jr., Powars, D.S., and
Gohn, G.S., eds., Studies of the Chesapeake Bay impact
structure – The USGS-NASA Langley corehole, Hampton,
Virginia, and related coreholes and geophysical surveys:
U.S. Geological Survey Professional Paper 1688, p. K1K32.
January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
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Montanari A. and Koeberl C.,
Impact stratigraphy: The Italian record,
Berlin: Springer. 364 p. 2000,
ISBN: 354066368.
|
Paillet, F.L., and Cheng, C.H.,
Acoustic Waves in Boreholes,
CRC Press, Boca Raton, Florida, 264 p. 1991,
ISBN: 0849388902.
|
Poag, C. W., Koeberl, C., and Reimold, W. U.,
The Chesapeake Bay Crater. Geology and Geophysics of
a Late Eocene Submarine Impact Structure. Impact
Studies Series. XV, 522 p., 2003, CD-ROM.
Berlin, Heidelberg, New York: Springer-Verlag,
ISBN: 3540404414 ; DOI: 10.1017/S0016756805260430
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Powars, D.S., and Bruce, T.S., 1999,
The effects of the ChesapeakeBay impact crater on
the geological framework andcorrelation of
hydrogeologic units of the lower York-James
Peninsula, Virginia:
U.S. Geological Survey Professional Paper 1612, 82
p.
|
Powars, D.S., 2000,
The effects of the Chesapeake Bay impact crater on
the geological framework and correlation of
hydrogeologic units of southeastern Virginia, south
of the James River:
U.S. Geological Survey Professional Paper 622, 53
p.
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January 17, 2008: IAP 2008 12.091 SESSION 4: P.ILA
| Powars, D.S., Bruce, T.S., Bybell, L.M., Cronin, T.M.,
Edwards, L.E., Frederiksen, N.O., Gohn, G.S., Horton,
J.W., Jr., Izett, G.A., Johnson, G.H., Levine, J.S.,
McFarland,E.R., Poag, C.W., Quick, J.E., Schindler, J.S.,
Self-Trail,J.M., Smith, M.J., Stamm, R.G., and Weems,
R.E., 2001,
Preliminary geologic summary for the USGS–NASA
Langley corehole, Hampton, Virginia,
U.S. Geological Survey Open-File Report 01–87–B, 20 p.
2001.
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Shaw H. F. and Wasserburg G. J.,
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